1. Field of the Invention
The invention relates generally to drilling machine guidance systems and, more particularly, but not by way of limitation, it relates to an improved calibration system for use with a push drill guidance system as utilized in horizontal drilling operations.
2. Description of the Prior Art
There are numerous prior art guidance systems for use with drilling apparatus, both horizontal drilling machines and vertical or well drilling apparatus. U.S. Pat. No. 3,362,750 discloses a mining apparatus having programmed cutting direction and attitude controls, and this teaching utilizes a comparator for sensing a departure of the cutting machine from its programmed direction thereafter to correct the deviations. U.S. Pat. No. 3,326,008 relates to an electrical gopher which is utilized to bore horizontal cable holes. This device utilizes a plurality of synchro motors to maintain its guidance directions. Still other forms of circuitry are utilized in the prior art, especially that art which is related to position keeping within vertical boreholes and well drilling apparatus; however, none of the prior art approaches are similar to the present circuit apparatus nor do they offer the attendant functions and advantages for operation of a push drill remotely guided through a mineral stratum. U.S. Pat. No. 4,164,871 discloses an instrument package which is integrally connected into the push drill string for control communication back to an operator position. The system utilizes accelerometer sensing to determine pitch and roll of the drill instrument while gamma ray count is utilized to determine vertical positioning of the push drill relative to overlying and underlying rock formation, e.g., shale formations adjacent coal seams. Control signals are then processed in the instrument package for transmission back along a multiple conductor control cable to the operator position, whereupon output indication enables the operator to hydraulically control the push drill to accomplish attitude correction during progression through the mineral stratum.